1. Technical Field
The presently disclosed subject matter relates to lighting devices, and in particular, to lighting devices which include a substrate provided with a light source and a lens with a lens cut portion formed on a rear surface thereof, the lens cut portion being configured to control the illumination direction of the device.
2. Description of the Related Art
Known conventional lighting devices have a substrate, a lens (lens portion), and a light source (for example, an LED chip) disposed inside a lighting chamber (for example, a space) defined by the substrate and the lens (see, for example, Japanese Patent Application Laid-Open No. Sho 60-130001). This type of lighting device is shown in FIGS. 1A and 1B. As shown, the lighting device has a lens portion 50 which includes a lens cut portion 70 formed on a rear surface of the lens portion 50. The light includes light beams emitted from the light source 20 at a certain angle with respect to the main optical axis and which can be incident on the lens cut portion 70. Then, the light is reflected by the lens cut portion 70 to be projected in the illumination direction of the lighting device (upward in the drawing).
In this lighting device, light beams emitted from the light source 20 at a relatively small angle with respect to the main optical axis of the light source 20 can be incident on and be refracted by the lens cut portion 70 so as to be projected in the illumination direction of the lighting device. Light beams emitted from the light source 20 at a relatively large angle with respect to the main optical axis can be incident on the lens cut portion 70, but also reflected by the same so as to be projected in the illumination direction.
In the above configuration of the lighting device, when the lens 50 is formed of a resin material, corners of the lens cut portion 70 may not be able to take an acute shape due to some molding condition restrictions (for example, draft angle of a molding die or the like). In this case, the corners thereof may take a rounded shape (with a corner R).
As a result, when light beams are emitted from the light source at an angle of about 45° or the like with respect to the main optical axis of the light source, part of the light beams may not be refracted or reflected by the lens cut portion 70, but may be reflected by the front surface of the lens 50 to be directed to, and transmit through, the outer peripheral surface (side face 50a) of the lens 50. In this case, the light beams may be projected outside of the designated projection area. This may lower the light utilization efficiency. In addition, the projected light beams may become glare light.